Strain dependence of the performance enhancement in strained-Si n-MOSFETs

The first measurements of the strain dependence of the electron mobility enhancement in n-MOSFETs employing tensilely-strained Si channels are reported. For pseudomorphic Si films grown on relaxed-Si/sub 1-x/Ge/sub x/ layers, the mobility enhancement ratio is found to saturate at approximately 1.76 at room temperature for x on the order of 0.20. As the temperature is lowered, the mobility enhancements for all strain levels initially converge, and subsequently decrease, with no enhancement observed at cryogenic temperatures (/spl ap/5 K). Similar behavior is seen at higher drain fields in the device transconductance.<>